<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Counter</title>
</head>
<body>
    <div id="app">
        <div class="input_num" >
            <button @click="sub">
                -
            </button>

            <span>{{ num }}</span>

            <button @click="add">
                +
            </button>
        </div>

    </div>

    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
    
    <script>
        var app = new Vue({
            el: "#app",
            data:{
                num:1
            },
            methods: {
                add:function(){
                    // alert('+++')
                    if (this.num<10) {
                        this.num++;
                    } else {
                        alert('已到达最大值');
                    }
                },
                sub:function(){
                    if (this.num>0) {
                        this.num--;
                    } else {
                        alert('已到达最小值');
                    }
                }
            }
        })
    </script>
</body>
</html>